Sunday, January 16, 2011

Fermi Gamma Ray Space Telescope

I've said this here before but I have (apparently) some new readers so I'll explain again. When Ryan gets in trouble, real trouble rather than just little trouble (lying vs getting home late for instance), she gets assigned papers. This happens roughly once a year but I anticipate it happening more often as the rebellious teen years show up. I try to make the paper topic match the crime, but sometimes it's hard. Lying to a teacher in 3rd grade got her a paper on Watergate, for instance. But for not getting her homework done, I drew a blank. So here is, in its entirety, her paper on a giant telescope. For what it's worth, I don't understand a word of it.

Fermi Gamma Ray Space Telescope

By Ryan Tillman

The Fermi Gamma Ray Space Telescope is a space observatory being used to perform gamma ray astronomy observations from low Earth orbit. This report will cover the objectives, stages, discoveries, equipment, and general information of this research mission.

The main objective of this mission is to study the black hole jets aimed directly at Earth to find out whether they are composed of a combination of electrons and positrons or only protons. More objectives are: study gamma ray bursts with an energy range several times stronger than ever before so scientists can understand them better; study younger, more energetic pulsars, or highly magnetized, rotating neutron stars that emit beams of electromagnetic radiation, in the Milky Way than ever before so as to broaden our understanding of stars; study the pulsed emissions of magnetospheres, or the magnetic fields around celestial bodies, so as to possibly solve how they are produced; study how pulsars generate winds of interstellar particles; provide new data to help improve upon existing theoretical models of our own galaxy; study whether ordinary galaxies are responsible for gamma ray background radiation. The potential for a huge discovery awaits if ordinary sources are determined to be irresponsible, in which case the cause may be anything from self-annihilating dark matter to entirely new chain reactions among interstellar particles that have yet to be conceived.

On March 4, 2008, the spacecraft arrived at the Astrotech payload processing facility in Titusville, Florida. On June 4, 2008, after many previous delays, it was determined that Fermi would launch around June 11, as the last delays resulted from the need to replace the Flight Termination System batteries. Fermi launched successfully on June 11, 2008, departing from pad B at Cape Canaveral Air Force Station Space Launch Complex 17, and the spacecraft separated from its carrier rocket about 75 minutes afterward. Fermi currently resides in a low-Earth orbit at an altitude of 340 miles at an inclination of about 29 degrees.

The first major discovery came when the telescope discovered a pulsar in the CTA 1 supernova remnant that appeared to emit radiation in the gamma ray bands only, an unusual trait for its kind. This new pulsar sweeps the earth every 317 milliseconds at a distance of around 4,600 light years. Another important discovery came in September 2008, when the gamma ray burst GRB 080916C in the constellation Carina was recorded by the Fermi telescope. This burst is noted as having “The largest apparent energy release yet measured.” The explosion had the power of about 9,000 ordinary supernovae, and the relativistic jet of material ejected in the blast must have moved at a minimum of 99.9999% the speed of light. Overall, GRB 080916C had “the greatest total energy, the fastest motions, and the highest-energy initial emissions” ever seen.

Another round of discoveries came in 2010. In February 2010, it was announced that Fermi had determined that supernova remnants act as enormous accelerators for cosmic particles. This determination fulfills one of the stated objectives for this project. In March 2010, it was announced that active galactic nuclei are not responsible for most gamma ray background radiation. Though active galactic nuclei do produce some of the gamma ray radiation detected here on Earth, less than 30% originates from these sources. The search now is to locate the sources of the remaining 70% or so of all gamma rays detected. Possibilities include star forming galaxies, galactic mergers, and yet-to-be explained dark matter interactions. In November 2010, it was announced that two gamma ray and x-ray bubbles were detected around the Milky Way galaxy. The bubbles extend about 25,000 light years above and below the center of the galaxy. The galaxy's diffuse gamma ray fog hampered prior observations, but the discovery team worked around this problem.

Two important pieces of equipment are the Gamma ray Burst Monitor and the scintillators. The Gamma ray Burst Monitor detects sudden flares of gamma rays produced by gamma ray bursts and solar flares. The Gamma ray Burst Monitor results show that gamma rays and antimatter particles, or positrons, can be generated in powerful thunderstorms.The spacecraft's scintillators, or photon energy detectors, are on the sides of the spacecraft to view all of the sky which is not blocked by the earth. The design is optimal for good resolution in time and photon energy.

Another important piece of equipment is the Large Area Telescope, or LAT, which detects individual gamma rays using technology similar to that used in terrestrial particle accelerators. In the LAT, photons hit thin metal sheets, convert to electron-positron pairs, and pass through interleaved layers of silicon microstrip detectors, causing ionization, which producestiny pulses of electric charge. Researchers can combine information from several layers of this tracker to determine the path of the particles. After passing through the tracker, particles enter the calorimeter, which consists of a stack of caesium iodide scintillator crystals, to measure the total energy of the particles. The LAT's field of view is large, consisting of about 20% of the sky. The resolution of its images is modest by astronomical standards, a few arc minutes for the highest-energy photons and about 3 degrees at 100 MeV. The LAT is a bigger, better successor to the EGRET instrument on NASA's Compton Gamma Ray Observatory satellite in the 1990s. Several countries produced the components of the LAT, sending the parts for assembly at SLAC National Accelerator Laboratory. The participating institutions were:

Everything here, and a little bit more that won't fit on 3 pages, went into the building, maintaining, and fame of this marvelous spacecraft. I had to type a whole lot of French that I don't understand for that last part. Well, since I guess I'm doing the conclusion, I should do conclusiony stuff. This report listed the objectives, stages, discoveries, and equipment of this research mission. Bye!!!!!!!